1. Field of the Invention
The present invention relates to fastening devices for anchoring a sealing strip on a roof, and more particularly to fastening devices for a roof sealing strip in which a fastener penetrates a holder in the sealing strip so that the holder is pressed against the upper side of the sealing strip to anchor it on a roof.
2. Description of the Prior Art
Sealing strips, especially sealing strips placed on a flat roof and made of polyisobutylenes, polyvinyl chloride, bitumen, polymer bitumen or the like, must be fixed to the structure by means of mechanical fasteners in order to prevent being lifted by the wind. At least three fastening devices need to be provided per square meter of roof top in the center region of a building roof, more than ten in the corner region, and an inbetween quantity in the edge region.
The fastening devices are usually arranged in the edge region of a roof sealing strip and are tightly covered by the adjacent roof sealing strip, with a seam overlap of 10 cm to 12 cm being provided. Seam overlaps, especially roof sealing strips made of plastic, are a significant cost factor.
Since the fastening devices in a region must be distributed approximately evenly over the roof top, narrower roof sealing strips are placed in regions requiring a larger quantity of fastening devices, i.e., in corner and edge regions, than in the center region of a roof. The fastening devices are thus arranged parallel to the rows to be fastened extending along the edges of a roof sealing strip. Within certain limits, the distance between the fastening devices in a row to be fastened should correspond to the quantity of fastening devices required per square meter. A distance greater than 50 cm and a distance of less than 15 cm must be avoided in this case. The requirement to match different strip widths continues to be a relatively complicated problem to solve in practice.
The introduction of load in the covered edge region of mechanically fastened roof sealing strips is statically disadvantageous, since the introduction of load is asymmetric and thus requires additional efforts to secure them.
In order to eliminate these drawbacks, fastening devices were developed which may be installed at any desired location in a roof sealing strip. Fastening devices which penetrate the roof sealing strip (through strip fasteners) have proven to be successful.
U.S. Pat. No. 4,860,513 discloses such a fastening device for roof sealing strips comprising a disk-shaped holder and a through-opening arranged in the center. The wall of the through-opening is configured semi-circularly concave toward the udder side in order to receive the head of a screw which is semi-circular on its underside and serves as a fastener. On its upper side the head of the screw is provided with a hexagon socket. Due to the semi-circular fit of the screw head in the holder, the screw must be attached pivotably and perpendicularly in relation to the roof top. The head of the screw lies approximately on the plane of the roof sealing strip, so that in the region of the threaded joint, a relatively large hole must be punched out of the roof sealing strip. The screw, which is provided as a fastener has a hollow shaft, and in the region of the screw thread, bores, penetrating the walls of the fastener in the radial direction, are provided at the lower end of the fastener such that a sealing means may be pressed from the upper end of the fastener through the hollow shaft. However, in the known fastening device no seal is provided between the head of the fastening means and the holder.